1. Field of the Invention
The present invention relates to techniques of packaging electric circuit boards and, more specifically, to circuit board packaging hardware structures for packaging at high density into a full system an interconnected set of an increased number of computational modules using printed wiring circuit boards for large-scale, highly-advanced electronic digital equipment such as supercomputers adapted for massively parallel processing.
2. Description of the Related Art
With recent improvements in the performance and reliability of highly advanced electronic equipment such as massively parallel computers, the scale of electronic circuits used is becoming increasingly large. This will involve an increase in the number of circuit components. Although the integration density of semiconductor integrated-circuit (IC) devices is increasing and the capability of packing electronic circuits into an IC chip is also increasing, the enlargement of circuit scale exceeds the packing capability. In order to decrease the number of printed wiring boards used in electronic equipment as far as possible, a multilayer interconnection technique is applied to each board. The application of the multilayer interconnection technique increases the packaging density of semiconductor IC devices on each board, thus achieving an increased total packaging efficiency of electronic equipment.
However, the recent advances of technology impose unlimited requirements on further improvements in the existing high-density packaging technique. With the existing high-density packaging technique, it is a common practice to arrange a number of separate printed wiring boards in plane. For interconnection between adjacent ones of these boards, a connecting method called "back plane" or flexible flat connecting cables are used. The back-plane connection method is a technique of implementing interconnection of ordinary printed wiring boards each having a large number of IC devices mounted thereon.
Typically, a main board (mother board) having connector members, called "card edge connectors", attached to its peripheral edges is used. A printed wiring board is plugged, at its end whereat a connection pad train pattern is arranged, into the mother board, thereby obtaining electrical interconnection therebetween. The back-plane connection method, which eliminates the need of wiring connecting members between boards, can achieve a fairly high packaging density; however, the boards will require extra areas to form pad patterns for interconnection only at their corresponding peripheries. With the recent advance of high-density packaging, technology connection terminals required with boards have been increasing in number. An increase in the number of connection terminals results in an increase in the number of pads in a pad pattern of each board, which will undesirably increase the extra board area.
Naturally, manufacturing constraints are imposed on the size of printed wiring boards. If the extra board area for interconnection of printed wiring circuit boards were increased and no matter how internal electronic circuits were packed into a semiconductor IC chip successfully with a high density, an increase in the area of a resulting board would limit the efficiency in packaging a large number of boards in a full frame to a low level. This is a serious obstacle to the implementation of final high-density packaging of large-scale electronic equipment which system manufacturers have long desired.